a) Field of the Invention
The present invention relates to a wireless induction technology, and more particularly to an antenna structure of an RFID (Radio Frequency Identification System) transponder.
b) Description of the Prior Art
An RFID utilizes a reader to send out radio waves to a transponder in order to perform data identification, access and management. A working principle of the RFID utilizes a resonant circuit which is constituted by the antenna to emit or receive a radio signal that contains a chip identification code, to perform data identification and transmission. Therefore, the transponder can be widely applied in logistics management, production line automation, warehouse management, access control management, airport baggage management, smart tags and all kinds of stored value tickets or cards.
As shown in FIG. 1, an antenna 1 in a transponder is constituted by a conductive material, and a proper position of the conductive material is provided with a winding coupling part 2 and an RFIC (Radio Frequency Interface Chip) 3, with the aforementioned radio signal (resonant signal) that contains the chip identification code being produced by the RFIC 3 and transmitted back to a reader through the antenna 1 that is constituted by the conductive material.
The aforementioned RFIC 3 is electrically connected at a disconnection position of the winding coupling part 2 to switch on a circuit, allowing a control signal of the RFIC 3 to be transmitted onto the coupling part 2. However, as the aforementioned coupling part 2 is in a winding shape, a gap 4 is formed at the disconnection position, such that when the antenna 1 is emitting the radio signals, stronger directivity is available toward the gap 4 of the coupling part 2. Accordingly, in terms of an entire covering range of the signals, the covering range of the inducible signals will be smaller for the signals with the stronger directivity.
On the other hand, the antenna 1 of the RFID transponder is rarely provided with functions of near field induction (within 3 times of the wavelength of the radio wave) and far field induction (beyond 3 times of the wavelength of the radio wave) at a same time.
FIG. 2 shows a schematic view of a structure of another conventional dipole antenna, wherein a coupling part 2, which is made by a conductive material, of an antenna 1, is provided with a magnetic coupling element 5, with a capacitive coupling element 6 which contains an RFIC 3 being overlapped vertically on a corresponding position of the magnetic coupling element 5, so as to transmit the signals by a coupling effect of the magnetic coupling element 5 and the capacitive coupling element 6.
For this kind of antenna design that utilizes the capacitive coupling, such as that disclosed by the U.S. Pat. No. 7,158,033 B2, the magnetic coupling element 5 is required additionally to be provided on the antenna 1 to match with the capacitive coupling element 6. In addition, as the capacitive coupling element 6 and the magnetic coupling element 5 are overlapped correspondingly in the vertical direction, requirement to the structure is higher, and if no conductive regions or other corresponding methods are provided, then the issues of antenna directivity and the covering range of signals still cannot be solved.